The present invention is an improvement over the system and method described and claimed in U.S. Pat. No. 3,919,987, Haubner et al, assigned to the assignee of the present application. The system of the aforementioned patent provides a predetermined number of pulses within a given angle of rotation of a disk, coupled to a shaft of an internal combustion engine, by locating a predetermined number of magnetic discontinuities, for example teeth, at the circumference of the disk and sensing the passage of these discontinuities, or teeth, by means of a magnetically responsive transducer. This system, while eminently suitable for the purposes for which it was developed, requires a comparatively accurate transducer disk, accurately located on the shaft rotating with the engine. The number of discontinuities, for example teeth, on the disk determines the number of pulses sensed by the transducer.
Adjusting ignition timing by suitable changing of the ignition angle--with respect to angular position of the crankshaft of the engine--has substantial influence on the nature of combustion of the air-fuel mixture when the working or power stroke of the engine commences. Thus, both the power output as well as the nature of the exhaust emission are materially influenced by proper ignition timing. Increasingly severe requirements with respect to detoxification of exhaust gases require increasing accuracy in adjustment of ignition timing at all operating conditions of the engine. Mechanical ignition timing, and change of ignition timing, typically spark advance, while satisfactory in many respects does not, however, meet the requirements for accuracy which are continually demanded.
It is possible to compute the appropriate ignition timing angle by electronic calculation. Electronic arrangements additionally readily permit consideration of various external or ambient operating conditions or parameters, such as engine operating temperature, ambient temperature, loading on the engine, speed, and the like. Also, the actual composition of the exhaust gases, if sensed, can be considered and used as a control parameter to influence ignition timing.
The aforementioned U.S. Pat. No. 3,919,987 utilizes a system in which transduced signals are generated by a disk which has a predetermined number of magnetic discontinuities, located within a predetermined angular range thereof. A transducer generates an output which is a composite formed by a direct voltage with a superimposed alternate voltage. Manufacture of such transducer disks is comparatively expensive and complex; additionally, digital as well as analog signals due to interferences and the like may further modulate the signal derived from the transducer and lead to inaccuracies.